A balanced line in a wireless communication system may include a pair of conductive transmission lines, each of which are structurally symmetrical and have equal but opposite current along their respective lengths. Therefore, due to cancellation effects in the balanced line, no radiation occurs along the transmission lines, making it ideal for rejecting external noise. One implementation of the balanced line in a wireless system includes dipole antennas, for example.
In contrast, unbalanced lines, such as coaxial cable, which is designed to have its return conductor connected to ground, or circuits whose return conductor actually is ground, may have current differences within the coaxial cable, causing the transmission line to radiate.
A balun device may be used to achieve impedance compatibility between balanced line and unbalanced line. In addition, the balun may serve as an interface between a source and a device, which each have different impedance characteristics. In radio frequency (RF) applications, for example, balun devices may be used to achieve compatibility between balanced systems, such as a balanced antenna, and unbalanced systems, such as the coaxial cable. A variety of configurations exist to implement balun devices in antenna device applications.
In the appended figures, similar components and/or features may have the same reference numeral. Further, various components of the same type are distinguished by a second label following the reference numeral. If only the first reference numeral is used in the specification, the description is applicable to any one of the similar components having the same first reference numeral irrespective of the second reference numeral.